The present invention relates to geothermal energy production and, more particularly, to systems and methods of intelligently extracting heat from geothermal reservoirs.
Geothermal heat originating from the earth's core is a “renewable” source of energy. Briefly, the magma existing below the earth's crust heats nearby rocks and water, and hot geothermal effluent comprised of water and steam travels through faults and cracks to the earth's surface as geysers. Geysers in northern California are currently viable sources for geothermal energy plants. However, most hot geothermal water and heat stays deep underground trapped in geothermal reservoirs and must be brought to the surface via a drilled production well if it is to be productively used. A geothermal power plant is a thermal plant which uses the heat from geothermal reservoirs as its principal source for generation of electrical power. The geothermal effluent is heated in the geothermal reservoir and subsequently produced to the surface to power the geothermal power plant. The geothermal effluent most commonly used is water, which, in some applications, can phase transition into steam during the heat extraction process from the geothermal reservoir.
There are basically three kinds of geothermal power plants which utilize this hot water/steam in geothermal reservoirs as a geothermal effluent. A “dry” steam reservoir produces steam, but very little water. This steam is piped directly to a “dry” steam power plant to provide the force to spin a turbine generator. A second kind of plant, called a “flash” power plant, taps into a geothermal reservoir that produces mostly hot water ranging in temperatures between 200° F. and 300° F. This high temperature water is brought to the surface and, once released from the pressure of the reservoir, flashes into steam in a separator. The steam is then used to drive an adjacent turbine. In a third kind of plant, called a “binary” power plant, geothermal effluent between 250-360° F. is passed through a heat exchanger where its heat is transferred to a second (binary) liquid that boils at a lower temperature than the effluent. When heated, the binary liquid flashes to vapor which expands and spins turbine blades.
To more efficiently extract heat from geothermal reservoirs, the reservoirs are often fractured in order to provide enhanced fluid communication through the resulting fracture networks. The permeability of the resulting fracture network directly affects the heat transfer capability of the geothermal effluent as it circulates therethrough. What is needed is an intelligent means of extracting heat from fracture networks defined in geothermal reservoirs, and thereby provide a steady source of heat to a power plant arranged at the surface.